I made my own, cheap and fairly easy to do if you are a practical sort of person, they worked on a T2 so should work on an F75, check out my post in the headphones section, Wireless headphones for
under £20.

Really pleased with them, you can use your favorite headphone . We found that the receiver runs out of battery long before the transmitter due to it driving the large speakers in the over ear phones on long hunts. The beauty of this type is that if either go flat you just plug your headphones direct into the machine and carry on. Not something you can do with wireless headphones with built in batteries. Not experienced any noticeable lag